Seat cushions currently used in automotive, aircraft, and military vehicles are generally passive in nature. That is, they rely on the use of rate sensitive foams to cushion occupants and absorb energy from impacts, and from the catapult phase of an ejection in the case of aircraft. While these foams can reduce the probability of injury by slightly lowering the spinal loads that an occupant is exposed to, they have several limitations. First, they are very sensitive to environmental conditions such as temperature, humidity, and age. Each of these conditions reduces the effectiveness of the foams. As such, their performance can never be known or predicted accurately. In addition, their passive nature prevents them from adjusting to the contours of each individual or adjusting to a particular impact event.
With the increased tempo of military operations, including combat missions that can extend to 40 hours or more, such limitations can reduce air crew comfort and effectiveness. Moreover, current ejection seats create discomfort, soreness, and numbness. They also increase overall operator fatigue, particularly during extended missions. These conditions can adversely affect operator effectiveness.
Another limitation of passive cushions is that they only can absorb a certain amount of energy in a particular way and therefore cannot be designed to provide optimal support and energy absorption for different conditions such as different sized occupants and different impact levels. Typical designs of passive cushions are directed to mid-sized males. If a heavier person now uses the system, they may pre-compress the cushion beyond the point at which it has been designed to absorb any additional impact energy. Conversely, if a smaller person uses the system, they may not sufficiently load the system during impact to absorb the energy. These are inherent limitations found in current designs that use passive cushions and foams.